An all-silicon electro-optic modulator is a key component in electronic photonic integrated circuits. Carrier dispersion based electro-optic modulators on Silicon-On-Insulator substrates have been demonstrated based on a MOS capacitor, a PIN diode or a PN junction. However, in order to achieve high performance devices with high extinction ratio for high data rate on small silicon foot print, one needs to break the traditional tradeoff between speed and extinction ratio. MOS based devices can potentially scale in speed to many tens of Gbits/s; however the effective index change obtained is limited due to small overlap of the optical mode with carrier concentration change. On the other hand PIN based devices with laterally formed junctions provide high extinction ratio but are limited in speed due to the carrier injection dynamics. Hence a tradeoff exists between speed and extinction ratio due to the available electrooptic structures. The present invention is a device which achieves both high-speed and high-extinction ratio through a novel doping profile.